Abstract
Electrovibration is one of the key technologies in surface haptics. By inducing controlled electrostatic forces, the friction within a sliding contact between the human finger and a capacitive screen is modulated, which in turn gives effective tactile feedback to the user. Such powerful haptic displays can be built into mobile phones, tablets, navigation devices, games consoles and many other devices of consumer electronics. However, due to the layered structure and complex material of human skin, the underlying contact mechanical processes have not yet been fully understood. This work provides new continuum-based approaches to macroscopic modeling of the electro-adhesive frictional contact. A solution of pure normal contact between a human finger and a rigid, smooth plane under electroadhesion is derived by applying Shull's compliance method in the extended regime of large deformations. Based on these results and assuming pressure-controlled friction, a model for the sliding electro-adhesive contact is developed, which adequately predicts the friction force and coefficient of friction over the whole range of relevant voltages and applied normal forces. The experimentally observed area reduction caused by the tangential force is incorporated in a more empirical than profound contact mechanical way. This effect is studied with the help of a two-dimensional finite element model of the fingertip, assuming non-linear elastic material for the skin tissue. Although the simulations are restricted to non-adhesive tangential contacts, they show a significant reduction of the contact area, which is caused by large deformations of the non-linear elastic material around the distal phalanx. This result indicates that adhesion is only of secondary importance for the area reduction.
Highlights
Understanding contact mechanics and friction of human skin is a great challenge for the tribological community
Similar to the empirical formula (34) that we found for the contact length of the finite element model, the empirical quadratic law proposed by Sahli et al (2018) for the ridge contact area: AR (FT) = AR,0 − ηFT2 (43)
A solution was first obtained for pure normal contact under electroadhesion, which in particular includes the dependence of the ridge contact area on the normal force as well as the applied voltage
Summary
Understanding contact mechanics and friction of human skin is a great challenge for the tribological community. The approach proposed by Heß and Popov exploits the close analogy of electroadhesive contacts to classical adhesion theories based on van der Waals forces This model provides insufficient results with respect to the contact area as a function of the normal force, since the original theory by Johnson et al. Based on the resulting function of the ridge contact area in terms of applied voltage and normal force, an extended model for the sliding electro-adhesive contact is developed in Chapter Tangential Contact with Electroadhesion. This chapter begins with a study of the origins of the experimentally observed area reduction in frictional contact by means of adhesion theory and a nonadhesive two-dimensional finite element model of the fingertip accounting for the large deformations and non-linear elastic material behavior. By a comparison with the predefined relationships (5) and (6) the following parameters can be identified:
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
